(a) Field of the Invention
The present invention relates to a high reduction ratio objective lens system for ultra microfiche.
(b) Description of the Prior Art
With the recent development of ultra microfiche, objective lens systems having high reduction ratios and high resolution are demanded. The conventional objective lens systems for microfiche were designed for magnification ratios on the order of 1/150x.about.1/120x and small film sizes. Further, for a reason to facilitate to correct aberrations, such objective lens systems had long focal lengths about 6 mm and long total lengths, and optical paths were bent by using large numbers of reflecting mirrors for preventing said lens systems from having long total lengths as final lens products due to long distance to object to be photographed. The conventional objective lens systems of this type therefore required a large number of optical members. It is therefore desirable to select a focal length as short as possible so as to make it possible to minimize conjugate distance and design a compact objective lens system. When a short focal length is selected, however, angle of field is apt to be widened on the object side to aggravate offaxial aberration so far as film size is kept constant. Further, working distance is shortened in proportion to the focal length, thereby making the lens system rather difficult to handle. In an objective lens system having such a short focal length, it will be obliged to impart strong refractive power to each lens component, thereby causing such defects as aggravation in aberrations. In order to eliminate these defects, it will be required to increase the number of lens components composing an objective lens system, thereby increasing number of machining steps and manufacturing cost.